Fluid flow in a moving system of fluid is basically a square root function of differential pressure. Traditionally, fluid flow has been measured by determining the differential pressure between two points and essentially converting differential pressure to fluid flow. Typically, a differential pressure signal can be directed to a pressure gauge and a fluid flow scale may be provided on the pressure gauge where the indicator arm of the pressure gauge will be utilized to indicate fluid flow on the flow scale. Thus, for any given differential pressure, the pressure gauge will indicate flow. Because flow is a square root function of differential pressure, it follows that the flow scale associated with the pressure gauge is not linear. Thus it follows that the accuracy and precision of such a device at the lower end of the scale is not as great as the accuracy and precision at the upper end of the scale.
Moreover, conventional pneumatic instrumentation used to measure fluid flow has typically been provided with an amplifier valve of the type including mechanical linkages, levers, bellows, and other moving parts. Such amplifiers including mechanical linkages and moving parts are often sensitive to vibration and mounting position, and accordingly this gives rise to inaccuracy and imprecision. In addition, conventional instrumentation for measuring fluid flow are known to be relatively slow in response time with over shoot or "bobbling" on the output.